Wireless charging apparatus

ABSTRACT

Apparatuses and systems are provided for improving wireless power transmission for mobile devices. An enclosure for a mobile device may include a first electrical coil configured to establish a first wireless coupling with a transmitter coil of a power supply and a second electrical coil configured to establish a second wireless coupling with the first electrical coil and to establish a third wireless coupling with a receiver coil of a mobile device. A distance between the receiver coil and the transmitter coil may exceed a range over which the transmitter coil may be able to transfer power to the receiver coil via a single wireless coupling between the transmitter coil and the receiver coil. The first wireless coupling, the second wireless coupling, and the third wireless coupling, when established, may enable the transmitter coil to perform a wireless power transfer to the receiver coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 16/358,891, filed Mar. 20, 2019, and entitled“Wireless Charging Apparatus,” the content of which is incorporatedherein by reference in its entirety.

FIELD

Aspects described herein generally relate to wireless power transmissionin mobile devices. More specifically, aspects relate to improvingwireless charging capabilities of various mobile device enclosures.

BACKGROUND

The use of magnetic induction in wireless charging of mobile devices isconventional. In many instances, an enclosure (e.g., a case, wallet, orthe like) may be placed over the mobile device for protection. However,use of an enclosure may limit wireless charging capabilities with mobiledevices.

Accordingly, there exists a need for ways to improve wireless chargingcapabilities for mobile devices that are stored in such enclosures.

BRIEF SUMMARY

The following presents a simplified summary of various aspects describedherein. This summary is not an extensive overview, and is not intendedto identify key or critical elements or to delineate the scope of theclaims. The following summary merely presents some concepts in asimplified form as an introductory prelude to the more detaileddescription provided below.

To overcome limitations in the prior art described above, and toovercome other limitations that will be apparent upon reading andunderstanding the present specification, aspects described herein aredirected to apparatuses and systems for improving wireless chargingcapabilities of mobile devices stored in various enclosures.

A first aspect described herein provides a first electrical coilconfigured to establish a first wireless coupling with a transmittercoil of a power supply. The first aspect described herein also providesa second electrical coil configured to establish a second wirelesscoupling with the first electrical coil and to establish a thirdwireless coupling with a receiver coil of a mobile device. In one ormore instances, a distance between the receiver coil and the transmittercoil may exceed a range over which the transmitter coil is able totransfer power to the receiver coil via a single wireless couplingbetween the transmitter coil and the receiver coil. Additionally oralternatively, the distance between the receiver coil and thetransmitter coil may diminish power transfer between the transmittercoil and the receiver coil (e.g., cause slower charging). In one or moreinstances, the first wireless coupling, the second wireless coupling,and the third wireless coupling, when established, may enable thetransmitter coil to perform a wireless power transfer to the receivercoil. Additionally or alternatively, the first wireless coupling, thesecond wireless coupling, and the third wireless coupling, whenestablished, may increase the power transfer between the transmittercoil and the receiver (e.g., cause faster charging).

In one or more instances, the first electrical coil might not beconfigured to self-resonate. In these instances, a capacitor may beadded in parallel with the first electrical coil, which may cause thissub-circuit (e.g., paralleled coil and capacitor) to resonate at apredetermined frequency. In these instances, the second electrical coilmay include a second inductor and a second capacitor connected inparallel.

In one or more instances, the first electrical coil and the secondelectrical coil may be self-resonating coils. In one or more instances,the first electrical coil and the second electrical coil may beintegrated into one of: a mobile device case, a mobile device wallet,and a removable portion of a mobile device.

In one or more instances, wireless power transfer via the first wirelesscoupling, the second wireless coupling, and the third wireless couplingmay improve the power transfer and/or efficiency of the power transferrelative to that of a direct coupling between the transmitter coil andthe receiver coil. As a result, by implementing the first electricalcoil and the second electrical coil, the charging time of a battery maybe reduced.

A second aspect described herein provides a first electrical coilconfigured to establish a first wireless coupling with a transmittercoil of a power supply. The second aspect described herein furtherprovides a second electrical coil configured to establish a secondwireless coupling with a receiver coil of a mobile device. In one ormore instances, the first electrical coil and the second electrical coilmay be connected via a hard wire connection. In one or more instances, adistance between the receiver coil and the transmitter coil may exceed arange over which the transmitter coil may be able to transfer power tothe receiver coil via a single wireless coupling between the transmittercoil and the receiver coil. In one or more instances, the first wirelesscoupling and the second wireless coupling, when established, may enablethe transmitter coil to perform a wireless power transfer to thereceiver coil.

In one or more instances, the wireless power transfer to the receivercoil may be performed by causing mutual inductance between thetransmitter coil and the first electrical coil, and the secondelectrical coil and the receiver coil.

In one or more instances, the transmitter coil, the first electricalcoil, the second electrical coil, and the receiver coil may haveidentical outer diameters.

In one or more instances, the outer diameters may be greater than adistance between each of the respective coils. In one or more instances,the first electrical coil may include a first inductor connected inparallel to a first capacitor. In these instances, the second electricalcoil may include a second inductor connected in parallel to a secondcapacitor. In one or more instances, the first electrical coil may beconnected in parallel to the second electrical coil. In one or moreinstances, the first electrical coil and the second electrical coil maybe integrated into one of: a mobile device case, a mobile device wallet,and a removable portion of a mobile device.

A third aspect of described herein provides a power terminal configuredto provide a wireless power transfer to a mobile device when the mobiledevice is located within a baseline distance of the power terminal. Inone or more instances, a mobile device enclosure may be configured tohold the mobile device. In these instances, the mobile device enclosuremay include a first electrical coil, magnetically coupled to atransmitter coil of the power terminal, configured to receive thewireless power transfer from the transmitter coil. In these instances,the mobile device enclosure may also include a second electrical coilconfigured to receive the wireless power transfer from the firstelectrical coil. In one or more instances, the mobile device may includea receiver coil, may be magnetically coupled to the second electricalcoil, and may be configured to receive the wireless power transfer fromthe second electrical coil.

In one or more instances, the first electrical coil and the secondelectrical coil may enable the power terminal to provide the wirelesspower transfer to the mobile device when the mobile device is locatedwithin an updated distance of the power terminal, which may be greaterthan the baseline distance. In one or more instances, the firstelectrical coil may be magnetically coupled to the second electricalcoil. In one or more instances, the first electrical coil maymagnetically induce a current in the second electrical coil.

In one or more instances, the first electrical coil may be connected tothe second electrical coil via a hard wire connection. In one or moreinstances, the mobile device enclosure may include a battery, and thebattery in the mobile device enclosure may begin charging once themobile device has completed charging.

In one or more instances, the mobile device enclosure may be configuredto charge the mobile device, using the battery, based on determiningthat the mobile device is out of power, by inducing a current in thereceiver coil based on the second electrical coil. In one or moreinstances, the mobile device enclosure may be configured to store power,using the battery and without transmitting power to the mobile device,if the mobile device is not within the mobile device enclosure. Forexample, a user may place the mobile device enclosure on the wirelesscharging device without the mobile device, and the mobile deviceenclosure may begin charging without the mobile device.

In one or more instances, the mobile device enclosure may provide theenergy (e.g., from its battery) for the wireless power transfer to themobile device by magnetically inducing a current in the first electricalcoil based on the transmitter coil and magnetically inducing the currentin the receiver coil based on the second electrical coil.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of aspects described herein and theadvantages thereof may be acquired by referring to the followingdescription in consideration of the accompanying drawings, in which likereference numbers indicate like features, and wherein:

FIGS. 1A and 1B are diagrams illustrating a mobile device and a wirelesscharging device that may be used to implement aspects of the disclosure.

FIGS. 2A-2C are diagrams illustrating schematics for wireless powertransmission according to one or more aspects of the disclosure.

FIGS. 3A and 3B are diagrams illustrating a mobile device walletaccording to one or more aspects of the disclosure.

FIGS. 4A and 4B are diagrams illustrating a mobile device case accordingto one or more aspects of the disclosure.

FIGS. 5A-5D are diagrams illustrating the use of electrical coils withina mobile device enclosure according to one or more aspects of thedisclosure.

DETAILED DESCRIPTION

In the following description of the various embodiments, reference ismade to the accompanying drawings, which illustrate various embodimentsin which aspects described herein may be practiced. It is to beunderstood that other embodiments may be utilized and structural andfunctional modifications may be made without departing from the scope ofthe described aspects and embodiments. Aspects described herein arecapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein are for the purpose of description and shouldnot be regarded as limiting. Rather, the phrases and terms used hereinare to be given their broadest interpretation and meaning. The use of“including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. The use of the terms“mounted,” “connected,” “coupled,” “positioned,” “engaged” and similarterms, is meant to include both direct and indirect mounting,connecting, coupling, positioning and engaging.

FIG. 1A illustrates an example hardware environment 100 that may includea mobile device 105 and a wireless charging device 110. In one or moreinstances, the mobile device 105 may be a smart phone, tablet, smartwatch, or other electronic device capable of receiving a wirelesscharge. In these instances, the mobile device 105 may be configured toreceive a wireless charge from the wireless charging device 110. As isdescribed in greater detail below, the mobile device 105 may beconfigured to receive charge from the wireless charging device 110 usingmagnetic induction. In one or more instances, the wireless chargingdevice 110 may be a wireless charging pad, or the like, which may beconfigured to wirelessly charge a mobile device that is placed on thewireless charging device 110. In order to perform such wirelesscharging, the wireless charging device 110 may be connected to a powersource, such as a wall outlet, or may be configured to operate usingbattery power. Operations of the mobile device 105 and the wirelesscharging device 110 are described further below with regard to FIG. 1B.

Referring to FIG. 1B, the wireless charging device 110 may be connectedto a power source 110 a, such as a wall outlet, generator, battery, orthe like. In one or more instances, the power source 110 a may providealternating current (AC) to the wireless charging device 110.Additionally or alternatively, the power source 110 a may provide directcurrent (DC) to the wireless charging device 110 (e.g., if the powersource is a battery cell, or the like). In instances where alternatingcurrent is received by the wireless charging device 110 from the powersource 110 a, the wireless charging device 110 may route the current toan AC-DC converter to convert the alternating current into a directcurrent that may be used to charge various devices. In these instances,the wireless charging device 110 may perform an AC-DC-AC conversionprocess. Alternatively, the wireless charging device 110 may perform anAC-AC conversion using an AC-AC converter. In these instances, the AC-ACconverter may convert alternating current of a particular frequency andamplitude to a different frequency and amplitude without converting todirect current as an intermediate step. In either instance, the wirelesscharging device 110 may excite a transmitter of the wireless chargingdevice 110 with alternating current of a particular frequency andamplitude. In some instances, the wireless charging device 110 mayregulate the conversion process (e.g., ensure voltage and/or current arewithin a predetermined range, or the like). In one or more instances,the wireless charging device 110 may use a rectifier circuit 110 b toconvert the alternating current into a direct current. After convertingthe alternating current to direct current, the wireless charging device110 may use an inverter, such as inverter 110 c, to convert the directcurrent back to alternating current. In one or more instances, thewireless charging device 110 may perform this double conversion (e.g.,AC to DC and back again) to properly regulate incoming and outgoingvoltages, step up/step down the voltages, and/or to ensure theoperability of sensitive circuits that may be housed in the wirelesscharging device 110. The wireless charging device 110 may then route thealternating current to the transmitter coil 110 d. This may generate achanging magnetic field around the transmitter coil, which may be usedto generate current in another coil (e.g., receiver coil 105 c).

In one or more instances, when the mobile device 105 (and thus thereceiver coil 105 c) are located in close proximity to the wirelesscharging device 110 (e.g., laying on the wireless charging device 110),current may be generated in the receiver coil 105 c as a result of thechanging magnetic field surrounding the transmitter coil 110 d. As aresult, the receiver coil 105 c may be magnetically coupled to thetransmitter coil 110 d. Once the current is generated at the receivercoil 105 c, the mobile device 105 may feed the alternating currentthrough a rectifier 105 b to generate direct current. The mobile device105 may then store the energy at the battery 105 a (e.g., charge thebattery).

Accordingly, FIGS. 1A and 1B illustrate a conventional method ofperforming wireless charging between a mobile device and a wirelesscharging device. Such a method may adhere to the Qi standard (e.g.,version 1.2.4), developed by the Wireless Power Consortium, which statesthe following principles. 87 to 205 kHz is defined as the typical rangefor coil operating frequency. With regard to coil area, an outerdiameter of about 2 inches and 1.6 inches is standard for transmittersand receivers, respectively. To obtain an efficient power transfer, thetransmitter and receiver coils should be identical, the transmitter andreceiver coils should be aligned, the distance between the coils shouldbe small relative to an outer diameter of the coils, and magneticshielding may be used to reduce losses from magnetic field excitingelectrical currents in unintended coils/objects The elements ofefficient power transfer relating to distance between coils and coilalignment may cause problems for wireless charging of mobile devicesbecause the coil size may be limited by a size of the mobile device. Thefull standard is available at the Wireless Power Consortium website formembers of the organization.

FIG. 2A illustrates a coupling between the transmitter coil 110 d andthe receiver coil 105 c, as described above with regard to FIG. 1B(e.g., a basic transformer model). For example, the transmitter coil 110d may be modeled as a resistor 204 and an inductor 203. In one or moreinstances, the resistor 204 and the inductor 203 may be connected inseries. For example, the transmitter coil 110 d may have an inductanceof L_(T). The receiver coil 105 c may include a resistor 201 and aninductor 202. In one or more instances, the resistor 201 and theinductor 202 may be connected in series. In these instances, mutualinductance may be produced between the transmitter coil 110 d and thereceiver coil 105 c. In one or more instances, this mutual inductance(M) may be correlated with L_(T) and the inductance of the receiver coil105 c (L_(R)) via the following relationship:M=k√{square root over (L _(T) L _(R))}  (1)

In these instances, k may be a coupling coefficient, which may bedefined between 0 and 1. In one or more instances, as coil separationincreases and/or coil offset increases, mutual inductance and thecoupling coefficient between the coils may decrease. In these instances,a leakage inductance may be produced, as described below with regard toFIG. 2B.

FIG. 2B illustrates the aforementioned leakage inductance resulting fromincreased coil separation. For example, as a distance between thetransmitter coil 110 d and the receiver coil 105 c is increased, thetransmitter coil 110 d may produce a magnetic inductance (nM) 207. Inthese instances, n may refer to a turns ratio between the transmittercoil 110 d and the receiver coil 105 c (e.g., a ratio of a number ofloops forming each of the transmitter coil 110 d and the receiver coil105 c). In these instances, the leakage inductance 206 at thetransmitter coil 110 d may be determined using the followingrelationship:Leakage inductance 206=L _(T) −nM  (2)

In addition, in these instances, the receiver coil 105 c may produce aleakage inductance 205. This leakage inductance 205 at the receiver coil105 c may be determined using the following relationship:

$\begin{matrix}{{{Leakage}\mspace{14mu}{inductance}\mspace{14mu} 205} = {L_{R} - \frac{M}{n}}} & (3)\end{matrix}$

In these instances, the coupling coefficient may decrease. Accordingly,unless increased, the current in the transmitter coil 110 d and thereceiver coil 105 c might not be high enough to excite magnetizinginductance to produce a desired power output (e.g., to charge the mobiledevice 105). In these instances, as coil separation increases,efficiency of the wireless power transfer between the transmitter coil110 d and the receiver coil 105 c may decrease. FIG. 2C, describedbelow, presents modifications to the transmitter coil 110 d and thereceiver coil 105 c that may improve the efficiency of the wirelesspower transfer.

Referring to FIG. 2C, a schematic is shown that may provide a moreefficient wireless power transfer than the schematic in FIG. 2B. Forexample, such efficiency may be improved through resonant based magneticinduction. Accordingly, a discrete capacitor 209 may be added to thetransmitter coil 110 d and/or the transmitter coil 110 d may have aninherent distributed capacitance by design. Similarly, a discretecapacitor 208 and/or a specific amount of capacitance may be added tothe receiver coil 105 c. In one or more instances, an ideal amount ofcapacitance may be a function of coil parameters, coil coupling,receiver load, operating frequency, or the like corresponding to thediscrete capacitor 208 and the discrete capacitor 209. In theseinstances, the ideal capacitance may be determined via the followingrelationship:

$\begin{matrix}{C = \frac{1}{w^{2}L_{L}}} & (4)\end{matrix}$

In instances where the transmitter coil 110 d is identical to thereceiver coil 105 c, w may be an angular frequency and L_(L) may be thecoil leakage inductance. In one or more instances, a coupling betweenthe transmitter coil 110 d and the receiver coil 105 c might not befixed and/or well controlled. In these instances, the ideal capacitancemay be unknown. As a result, the transmitter coil 110 d may tune anoperating frequency in real time based on feedback from the receivercoil 105 c during resonant based magnetic induction. In these instances,the transmitter coil 110 d and the receiver coil 105 c may be configuredin accordance with the Qi standard or some other open or proprietarywireless power transfer standard, and may be configured to supportefficient power transfer over a range of relative coil positions throughthe use of an allocated frequency range.

Such techniques for wireless power transfer may be used in the chargingof wireless client devices such as the mobile device 105. However,problems may arise through implementation of these techniques in varioussituations as discussed below.

FIG. 3A illustrates a first wireless charging device enclosureembodiment. For example, in some instances, a user may keep the mobiledevice 105 in a mobile device wallet 305. This mobile device wallet 305may be used to provide protection for the mobile device 105 and may holdadditional personal items (e.g., a credit card, cash, driver's license,or the like). Although the mobile device wallet 305 may provide numerousbeneficial purposes, it may cause difficulty in wireless charging asshown below with regard to FIG. 3B.

Referring to FIG. 3B, which shows the mobile device 105, inside of themobile device wallet 305, laying on the wireless charging device 110 forpurposes of receiving a wireless power transfer. As is evident from FIG.3B, the mobile device wallet 305 may increase a distance between thewireless charging device 110 and the mobile device 105. As describedabove, increasing this distance may, in some instances, cause wirelesscharging to occur at a reduced efficiency level (e.g., when compared toa scenario where the mobile device 105 is place directly on the wirelesscharging device without the mobile device wallet 305). For example, ahigher leakage inductance may be generated in these instances. In otherinstances, increasing this distance may move the mobile device 105outside of a range within which the wireless charging device 110 mayprovide power. Additionally or alternatively, the material making up themobile device wallet 305 may also impede the wireless power transfer. Ineach scenario, the mobile device wallet 305 negatively affects thewireless power transfer between the wireless charging device 110 and themobile device 105.

FIG. 4A illustrates a second wireless charging device enclosureembodiment. For example, in some instances, a user may keep the mobiledevice 105 in a mobile device case 405. Similar to the mobile devicewallet 305, the mobile device case 405 may be used to provide protectionfor the mobile device 105, but may be smaller and less cumbersome thanthe mobile device wallet 305. In one or more instances, the mobiledevice case 405 may cause difficulty in wireless charging for similarreasons to those described above with regard to the mobile device wallet305, and as shown below with regard to FIG. 4B.

Referring to FIG. 4B, which shows the mobile device 105, inside of themobile device case 405, laying on the wireless charging device 110 forpurposes of receiving a wireless power transfer. As is evident in FIG.4B, the mobile device case 405 may increase a distance between thewireless charging device 110 and the mobile device 105. As describedabove, increasing this distance may, in some instances, cause wirelesscharging to occur at a reduced efficiency level (e.g., when compared toa scenario where the mobile device 105 is placed directly on thewireless charging device without the mobile device case 405). Forexample, a higher leakage inductance may be generated in theseinstances. In other instances, increasing this distance may move themobile device 105 outside of a range within which the wireless chargingdevice 110 may provide power. Additionally or alternatively, thematerial making up the mobile device case 405 may also impede thewireless power transfer. In each scenario, the mobile device case 405negatively affects the wireless power transfer between the wirelesscharging device 110 and the mobile device 105.

FIGS. 5A-5C illustrate a solution to the problems described herein withregard to wireless charging of mobile devices. Referring to FIG. 5A, anarrangement of the mobile device 105, the wireless charging device 110,and a mobile device enclosure 505 is described. In this arrangement, themobile device 105 may be laying on the wireless charging device 110 andthe mobile device enclosure 505 may form a layer between the mobiledevice 105 and the wireless charging device 110 such that the mobiledevice 105 is not directly touching the wireless charging device 110. Inone or more instances, the mobile device enclosure 505 may be a mobiledevice wallet (e.g., mobile device wallet 305), a mobile device case(e.g., mobile device case 405), or the like. As described above withregard to FIG. 1B, the mobile device 105 may include a receiver coil 105c and the wireless charging device 110 may include a transmitter coil110 d. To address the problems associated with wireless charging in thepresence of a mobile device enclosure (e.g., due to the increaseddistance between the mobile device 105 and the wireless charging device110, a type of material of the wireless charging enclosure, or thelike), two electrical coils may be added to the mobile device enclosure505. In these instances, a first electrical coil 505 a and a secondelectrical coil 505 b may be integrated into the mobile device enclosure505.

In one or more instances, dimensions of the first electrical coil 505 aand the second electrical coil 505 b may be substantially the same, andmay be an average between the dimensions of the transmitter coil 110 dand the receiver coil 105 c. In these instances, the transmitter coil110 d and the receiver coil 105 c may be manufactured and/or designed bydifferent entities (e.g., a phone enclosure manufacturer, a wirelesscharging station manufacturer, or the like), and thus dimensions of thetransmitter coil 110 d and the receiver coil 105 c may be different. Inthese instances, for example, diameters, number of windings, or the likeof the first electrical coil 505 a and the second electrical coil 505 bmay be an average of the diameters, number of windings, or the like ofthe transmitter coil 110 d and the receiver coil 105 c. In otherinstances, the transmitter coil 110 d and the receiver coil 105 c mayhave substantially the same dimensions, and thus the dimensions of thefirst electrical coil 505 a and the second electrical coil 505 b may besubstantially the same as the dimensions of the transmitter coil 110 dand the receiver coil 105 c. In these instances, the transmitter coil110 d and the receiver coil 105 c may establish a stronger wirelesscoupling with the first electrical coil 505 a and the second electricalcoil 505 b, respectively, than instances in which the transmitter coil110 d and the receiver coil 105 c have different dimensions than thefirst electrical coil 505 a and the second electrical coil 505 b.Further, in these instances, each of the first electrical coil 505 a andthe second electrical coil 505 b may be self-resonating coils.

In one or more instances, dimensions of the first electrical coil 505 aand the second electrical coil 505 b may be based on a size of themobile device enclosure 505. For example, if a first mobile deviceenclosure is larger than a second mobile device enclosure, the firstmobile device enclosure may have larger electrical coils than the secondmobile device enclosure. In one or more instances, dimensions of thefirst electrical coil 505 a and the second electrical coil 505 b may bebased on the recommendations and criteria of the Qi standard.

In one or more instances, a wire thickness of the first electrical coil505 a and the second electrical coil 505 b may be substantially thesame, and may be selected to minimize loss due to ohmic heating. Inthese instances, the wire thickness may be chosen based on therecommendations and criteria of the Qi standard.

In one or more instances, the first electrical coil 505 a and the secondelectrical coil 505 b may be integrated into the mobile device enclosure505 using conventional techniques for making and embedding radiofrequency identification (RFID) tags. For example, the first electricalcoil 505 a and the second electrical coil 505 b may be integrated into aflexible printed wiring board (PWB). In this example, the firstelectrical coil 505 a and the second electrical coil 505 b may beprinted onto the flexible PWB, and the flexible PWB may be integratedinto an outer layer of the mobile device enclosure 505. As anotherexample, the first electrical coil 505 and the second electrical coil505 b may be laminated and integrated into an outer layer of the mobiledevice enclosure 505.

. Accordingly, and as described further below with regard to FIGS.5B-5C, the wireless power transfer may occur from the transmitter coil110 d, through the first electrical coil 505 a and the second electricalcoil 505 b, and into receiver coil 105 c of the mobile device 105,rather than merely from the transmitter coil 110 d and to the receivercoil 105 c through the mobile device enclosure 505. In one or moreinstances, by adding coils designed to resonate by themselves or withdiscrete capacitance added within, a practical range of wirelesscharging may be extended between the wireless charging device 110 andthe mobile device 105. Two embodiments of this design are furtherdescribed below with regard to FIGS. 5B and 5C.

Referring to FIG. 5B, power may flow into the wireless charging device110 from a power source, and alternating current in the transmitter coil110 d may result in a changing magnetic field at the transmitter coil110 d. This process is further described above with regard to FIG. 1B.Rather than causing mutual inductance between the transmitter coil 110 dand the receiver coil 105 c, as described above, mutual inductance maybe caused between the transmitter coil 110 d and the first electricalcoil 505 a, located in the mobile device enclosure 505. For example, thetransmitter coil 110 d and the first electrical coil 505 a may establisha wireless coupling. In one or more instances, the transmitter coil 110d and the first electrical coil 505 a may be magnetically coupled. Inone or more instances, the first electrical coil 505 a may be modeled asan inductor and a capacitor in parallel with the inductor coupled to thetransmitter coil 110 d. Once alternating current is induced in the firstelectrical coil 505 a, the first electrical coil 505 a may establishmutual inductance, a wireless coupling, and/or a magnetic coupling withthe second electrical coil 505 b, located in the mobile device enclosure505. In one or more instances, the second electrical coil 505 b mayinclude an inductor and a capacitor connected in parallel. Once currentis induced at the second electrical coil 505 b, the second electricalcoil 505 b may establish mutual inductance, wireless coupling, and/ormagnetic coupling with the receiver coil 105 c, resulting in inductionof current at the receiver coil 105 c, which may be used to charge abattery at the mobile device 105. Accordingly, by channeling power tothe receiver coil 105 c, the first electrical coil 505 a and the secondelectrical coil 505 b may improve the efficiency of power transfer.

It should be understood that although FIG. 5B shows the first electricalcoil 505 a and the second electrical coil 505 b stacked on top of eachother, in one or more instances, the first electrical coil 505 a and thesecond electrical coil 505 b might not be stacked on top of each other,yet may still establish a wireless coupling. For example, in someinstances, the first electrical coil 505 a and the second electricalcoil 505 b may be located side by side. However, small proximity betweenthe first electrical coil 505 a and the second electrical coil 505 b,and close alignment of their respective axes may increase strength ofthe wireless coupling between the first electrical coil 505 a and thesecond electrical coil 505 b.

Furthermore, effects of a material of the mobile device enclosure 505 oninduction may be reduced by shortening the distance over which mutualinduction occurs. This may decrease both the efficiency and practicalrange of wireless charging for mobile devices enclosed by a case,wallet, or the like. Additionally, detrimental effects from theproximity of undesired materials may be reduced through the use offrequency tuning, as described in the Qi standard. In one or moreinstances, the transmitter coil 110 d may tune the frequency based onfeedback from the receiver coil 105 c. In these instances, thetransmitter coil 110 d may optimize the frequency in real-time using oneor more algorithms. For example, the transmitter coil 110 d may perturbthe frequency and determine whether it increased or decreased powertransfer. In this example, if the transmitter coil 110 d determines thatthe power transfer was increased, the transmitter coil may maintain thenew frequency. If the transmitter coil 110 d determines that the powertransfer was decreased, the transmitter coil 110 d may perturb thefrequency in the opposite direction. FIG. 5C illustrates a similarwireless charging configuration to that described above with regard toFIG. 5B. However, rather than causing mutual induction between the firstelectrical coil 505 a and the second electrical coil 505 b at the mobiledevice enclosure 505 (as shown in FIG. 5B), FIG. 5C illustrates anembodiment in which the first electrical coil 505 a is connected to thesecond electrical coil 505 b via a hard wire connection. In one or moreinstances, the wireless power transfer occurring via the configurationshown at FIG. 5C may be more efficient that the wireless power transferoccurring via the configuration shown at FIG. 5B because the current mayflow directly to the second electrical coil 505 b through a hard wirerather than depending on a wireless coupling between the firstelectrical coil 505 a and the second electrical coil 505 b.

Accordingly, by implementing the configurations shown in FIGS. 5B and5C, the practical range for charging a mobile device, associated with amobile device enclosure, via wireless charging may be extended.

In one or more instances, as shown in FIG. 5D, the mobile deviceenclosure 505 described above may also be configured with a battery 505c that may receive and store charge under certain situations. Forexample, the mobile device enclosure 505 may include the firstelectrical coil 505 a, the second electrical coil 505 b, and the battery505 c. If the mobile device 105 reaches a complete charge, the battery505 c may begin to charge. Accordingly, in some instances, when themobile device 105 is removed from the wireless charging device 110, itmay begin receiving charge from the battery 505 c if the mobile device105 is at less than full charge. Similarly, in one or more instances,the mobile device 105 might not be in the mobile device enclosure 505.In these instances, the mobile device enclosure 505 may still be placedon the wireless charging device 110, and may be configured to wirelesslyreceive and store a charge. For example, as described above, mutualinductance may be caused between the transmitter coil 110 d and thefirst electrical coil 505 a, located in the mobile device enclosure 505.The first electrical coil 505 a may be either magnetically coupled orconnected via a hard wire connection to the second electrical coil 505b. In either case, power may be transferred from the first electricalcoil 505 a to the second electrical coil 505 b, and then subsequently tothe battery 505 c.

Although the figures and description herein primarily describe a mobiledevice enclosure (e.g., a case, wallet, or the like) to house the firstelectrical coil 505 a and the second electrical coil 505 b, it should beunderstood that the first electrical coil 505 a and the secondelectrical coil 505 b may be embedded into a detachable portion of amobile device (e.g., a detachable battery cover or the like). Forexample, the first electrical coil 505 a and the second electrical coil505 b may be located in the detachable portion of the mobile device 105,and may be used to perform a wireless power transfer as describedherein. Additionally, the first electrical coil 505 a and the secondelectrical coil 505 b may be implemented in any other way so as to causethe first electrical coil 505 a and the second electrical coil 505 b tobe placed between the transmitter coil 110 d and the receiver coil 105c. Additionally, it should be understood that although the embodimentsdescribed herein utilize two electrical coils in the mobile deviceenclosure, it should be understood that other numbers of electricalcoils (e.g., one coil, three coils, or the like) may be implemented inthe mobile device enclosure to maximize charging capabilities (e.g.,based on dimensions, parameters, or the like corresponding to the mobiledevice enclosure). For example, in one or more instances, the mobiledevice enclosure may include a third electrical coil in addition to thefirst electrical coil 505 a and the second electrical coil 505 b. Inthese instances, the second electrical coil 505 b may establish awireless coupling with the third electrical coil and induce a current inthe third electrical coil. Alternatively, the third electrical coil maybe connected to the second electrical coil 505 b via a hard wireconnection, and current may flow directly from the second electricalcoil 505 b to the third electrical coil. In either instance, the thirdelectrical coil may establish a wireless coupling with the receiver coil105 c in the mobile device 105, and may induce a current in the receivercoil 105 c. Accordingly, the wireless charging device 110 may charge themobile device 105 through the mobile device enclosure 505 (e.g., throughfirst electrical coil 505 a, the second electrical coil 505 b, and thethird electrical coil), in a similar method as described above withregard to the two coil configuration.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An apparatus comprising: a first electrical coilconfigured to establish a first wireless coupling with a transmittercoil of a power supply; and a second electrical coil configured toestablish a second wireless coupling with the first electrical coil andto establish a third wireless coupling with a receiver coil of a mobiledevice, wherein: a distance between the receiver coil and thetransmitter coil exceeds a range over which the transmitter coil is ableto transfer power to the receiver coil via a single wireless couplingbetween the transmitter coil and the receiver coil, the first wirelesscoupling, the second wireless coupling, and the third wireless coupling,when established, enable the transmitter coil to perform a wirelesspower transfer to the receiver coil, and a number of windings of thefirst electrical coil and the second electrical coil is an average of anumber of windings for the receiver coil and a number of windings forthe transmitter coil, wherein the number of windings for the receivercoil is different than the number of windings for the transmitter coil.2. The apparatus of claim 1, wherein the first electrical coil isconnected in parallel with a capacitor to create a sub-circuit, andwherein the capacitor causes the sub-circuit to resonate at apredetermined frequency.
 3. The apparatus of claim 1, wherein the firstelectrical coil and the second electrical coil are integrated into oneof: a mobile device case, a mobile device wallet, and a removableportion of the mobile device.
 4. The apparatus of claim 1, wherein thefirst electrical coil and the second electrical coil compriseself-resonating coils.
 5. The apparatus of claim 1, wherein wirelesspower transfer via the first wireless coupling, the second wirelesscoupling, and the third wireless coupling occurs with a first leakageinductance and wherein the first leakage inductance is less than asecond leakage inductance corresponding to wireless power transfer via asingle wireless coupling between the transmitter coil and the receivercoil.
 6. The apparatus of claim 1, wherein a diameter of the firstelectrical coil and the second electrical coil is an average of adiameter for the receiver coil and a diameter for the transmitter coil.7. The apparatus of claim 1, wherein a diameter of the first electricalcoil, a diameter of the second electrical coil, a diameter for thereceiver coil, and a diameter for the transmitter coil are greater thana distance between each of the first electrical coil, the secondelectrical coil, the receiver coil, and the transmitter coil.
 8. Anapparatus comprising: a first electrical coil configured to establish afirst wireless coupling with a transmitter coil of a power supply; and asecond electrical coil configured to establish a second wirelesscoupling with a receiver coil of a mobile device, wherein: the firstelectrical coil and the second electrical coil are connected via a hardwire connection; a distance between the receiver coil and thetransmitter coil exceeds a range over which the transmitter coil is ableto transfer power to the receiver coil via a single wireless couplingbetween the transmitter coil and the receiver coil; the first wirelesscoupling and the second wireless coupling, when established, enable thetransmitter coil to perform a wireless power transfer to the receivercoil; and a number of windings of the first electrical coil and thesecond electrical coil is an average of a number of windings for thereceiver coil and a number of windings for the transmitter coil whereinthe number of windings for the receiver coil is different than thenumber of windings for the transmitter coil.
 9. The apparatus of claim8, wherein performing the wireless power transfer to the receiver coilcomprises: causing mutual inductance between: the transmitter coil andthe first electrical coil, and the second electrical coil and thereceiver coil.
 10. The apparatus of claim 8, wherein: the firstelectrical coil comprises a first inductor connected in parallel to afirst capacitor; the second electrical coil comprises a second inductorconnected in parallel to a second capacitor; and the first electricalcoil is connected in parallel to the second electrical coil.
 11. Theapparatus of claim 8, wherein the first electrical coil and the secondelectrical coil are integrated into one of: a mobile device case, amobile device wallet, and a removable portion of the mobile device. 12.A system comprising: a power terminal configured to provide a wirelesspower transfer to a mobile device when the mobile device is locatedwithin a baseline distance of the power terminal; and a mobile deviceenclosure configured to hold the mobile device, wherein the mobiledevice enclosure comprises: a first electrical coil, magneticallycoupled to a transmitter coil of the power terminal, configured toreceive the wireless power transfer from the transmitter coil; and asecond electrical coil configured to receive the wireless power transferfrom the first electrical coil, wherein the mobile device comprises areceiver coil, magnetically coupled to the second electrical coil,configured to receive the wireless power transfer from the secondelectrical coil, and wherein a number of windings of the firstelectrical coil and the second electrical coil is an average of a numberof windings for the receiver coil and a number of windings for thetransmitter coil, wherein the number of windings for the receiver coilis different than the number of windings for the transmitter coil. 13.The system of claim 12, wherein the first electrical coil and the secondelectrical coil enable the power terminal to provide the wireless powertransfer to the mobile device when the mobile device is located withinan updated distance of the power terminal, wherein the updated distanceis greater than the baseline distance.
 14. The system of claim 12,wherein the first electrical coil is magnetically coupled to the secondelectrical coil.
 15. The system of claim 14, further comprisingmagnetically inducing, using the first electrical coil, a current in thesecond electrical coil.
 16. The system of claim 12, wherein the firstelectrical coil is connected to the second electrical coil via a hardwire connection.
 17. The system of claim 12, wherein the mobile deviceenclosure includes a battery, and wherein the mobile device enclosure isfurther configured to begin charging, using the battery, once the mobiledevice has completed charging.
 18. The system of claim 17, wherein themobile device enclosure is configured to charge the mobile device, usingthe battery, based on determining that the mobile device is out ofpower, wherein the mobile device enclosure charges the mobile device byinducing a current in the receiver coil based on the second electricalcoil.
 19. The system of claim 17, wherein the mobile device enclosure isconfigured to store power, using the battery and without transmittingpower to the mobile device, if the mobile device is not within themobile device enclosure.
 20. The system of claim 12, wherein providingthe wireless power transfer to the mobile device comprises: magneticallyinducing a current in the first electrical coil based on the transmittercoil; and magnetically inducing the current in the receiver coil basedon the second electrical coil.